Universality of the Collins-Soper-Sterman nonperturbative function in gauge boson production

We revise the $b_*$ model for the Collins-Soper-Sterman resummed form factor to improve description of the leading-power contribution at nearly nonperturbative impact parameters. This revision leads to excellent agreement of the transverse momentum resummation with the data in a global analysis of Drell-Yan lepton pair and Z boson production. The nonperturbative contributions are found to follow universal quasi-linear dependence on the logarithm of the heavy boson invariant mass, which closely agrees with an estimate from the infrared renormalon analysis.Comment: published version; 14 pages, 4 figures, additional discussio

A new atmospheric aerosol phase equilibrium model (UHAERO): organic systems

In atmospheric aerosols, water and volatile inorganic and organic species are distributed between the gas and aerosol phases in accordance with thermodynamic equilibrium. Within an atmospheric particle, liquid and solid phases can exist at equilibrium. Models exist for computation of phase equilibria for inorganic/water mixtures typical of atmospheric aerosols; when organic species are present, the phase equilibrium problem is complicated by organic/water interactions as well as the potentially large number of organic species. We present here an extension of the UHAERO inorganic thermodynamic model (Amundson et al., 2006c) to organic/water systems. Phase diagrams for a number of model organic/water systems characteristic of both primary and secondary organic aerosols are computed. Also calculated are inorganic/organic/water phase diagrams that show the effect of organics on inorganic deliquescence behavior. The effect of the choice of activity coefficient model for organics on the computed phase equilibria is explored

Electron drift velocity in N2O in strong electric fields determined from rf breakdown curves

We report measurements of the breakdown curves of an rf capacitive discharge in low pressure nitrous oxide. The electron drift velocity was determined from the locations of the turning point and of the minimum in the breakdown curves in the range E/p = 87–840 Vcm−1 Torr−1. We compare our results with values calculated from the published cross-sections in the range E/p = 1–5000 Vcm−1 Torr−1 and find good agreement

Low-pressure gas breakdown in dual-frequency RF electric fields in nitrogen

This paper reports the recorded breakdown curves for dual-frequency (27.12MHz/2MHz and 13.56MHz/50Hz) discharges in nitrogen. Applying the LF voltage shifts the RF breakdown curve to the region of higher voltages and gas pressures, which is associated with the increased loss of charged particles due to the drift in the LF field. At higher LF voltage amplitudes the LF field contributes to gas ionization, the breakdown voltage for the RF discharge decreases and approaches zero when a self-sustained discharge in the LF field ignites. Applying the RF voltage leads to the decrease in the breakdown LF voltage, possibly due to the decrease of electron losses because of the oscillations in the RF field

The Effect of Discharge Chamber Geometry on the Characteristics of Low-Pressure RF Capacitive Discharges

We report the measured extinction curves and current–voltage characteristics (CVCs) in several gases of RF capacitive discharges excited at 13.56 MHz in chambers of three different geometries: 1) parallel plates surrounded by a dielectric cylinder (“symmetric parallel plate”); 2) parallel plates surrounded by a metallic cylinder (“asymmetric confined”); and 3) parallel plates inside a much larger metallic chamber (“asymmetric unconfined”), similar to the gaseous electronics conference reference cell. The extinction curves and the CVCs show differences between the symmetric, asymmetric confined, and asymmetric unconfined chamber configurations. In particular, the discharges exist over a much broader range of RF voltages and gas pressures for the asymmetric unconfined chamber. For symmetric and asymmetric confined discharges, the extinction curves are close to each other in the regions near the minima and at lower pressure, but at higher pressure, the extinction curve of the asymmetric confined discharge runs at a lower voltage than the one for the discharge in a symmetric chamber. In the particular cases of an “asymmetric unconfined chamber” discharge or “asymmetric confined” one, the RF discharge experiences the transition from a “weak-current” mode to a “strong-current” one at lower RF voltages than is the case for a “symmetric parallel-plate” discharge

Electron drift velocity in silane in strong electric fields determined from rf breakdown curves

We report measurements of the breakdown curves of an rf capacitive discharge in low pressure silane. The electron drift velocity was determined from the locations of the turning point and of the minimum in the breakdown curves in the range E/p = 145–1292 Vcm−1 Torr−1. We compare our results to values calculated from the published cross-sections in the range E/p = 1–2000 Vcm−1 Torr−1 and data calculated in other papers and find good agreement

Electron drift velocity in SF6 in strong electric fields determined from rf breakdown curves

This paper presents measurements of the electron drift velocity Vdr in SF6 gas for high reduced electric fields (E/N = 330–5655 Td (1 Td = 10−17 Vcm2)). The drift velocities were obtained using the method of Lisovskiy and Yegorenkov (1998 J. Phys. D: Appl. Phys. 31 3349) based on the determination of the pressure and voltage of the turning points of rf capacitive discharge breakdown curves for a range of electrode spacings. The Vdr values thus obtained were in good agreement with those calculated from the cross-sections of Phelps and Van Brunt (1988 J. Appl. Phys. 64 4269) using the BOLSIG code. The validity of the Lisovskiy–Yegorenkov method is discussed and we show that it is applicable over the entire E/N range where rf discharge ignition at breakdown occurs for rf frequencies of 13.56MHz or above

Modes of low-pressure dual-frequency (27/2 MHz) discharges in hydrogen

This paper studies the modes of dual-frequency (high-frequency (HF)/low-frequency (LF)) low-pressure discharges. The dual-frequency discharges are shown to burn in one of three possible modes. At small LF voltages the first mode is observed, i.e. the HF discharge perturbed by the LF voltage. The second mode, i.e. the combined discharge, exists in the presence of intense ionization in the sheaths, when the LF voltage exceeds some critical value. The third mode (the LF discharge perturbed by an HF field) is observed when a small HF voltage is applied to the burning LF discharge. The range of parameters within which the first mode of the combined discharge may be extinguished by the LF voltage increase is shown to be limited by the HF discharge extinction curve from the low-pressure side as well as the lowest HF voltage for the transition of the discharge from the first mode to the second one

A technique for evaluating the RF voltage across the electrodes of a capacitively-coupled plasma reactor

We propose a new technique for evaluating the RF voltage across the electrodes of low-pressure capacitively-coupled plasma reactors when direct measurements are not possible. It is based on determining the coordinates of the turning point in the RF breakdown curve and using known values of the electron drift velocity for the gas. The results are in good agreement with those obtained by direct measurements at the driven electrode. Furthermore it allows RF breakdown curves to be determined for different frequencies, giving results that are physically reasonable (coincidence of right-hand branches) and in agreement with other published results. The technique for determining RF voltage we proposed is valid when there is no discharge plasma between electrodes (e.g., before gas breakdown), as well as for negligibly small discharge currents (before extinction of the weak-current discharge mode)

Rf discharge dissociative mode in NF3 and SiH4

This paper shows that the rf capacitive discharge in NF3 and SiH4 can burn in three possible modes: weak-current α-mode, strong-current γ -mode and dissociative δ -mode. This new dissociative δ-mode is characterized by a high dissociation degree of gas molecules (actually up to 100% in NF3 and up to 70% in SiH4), higher resistivity and a large discharge current. On increasing rf voltage first we may observe a weak-current α-mode (at low NF3 pressure the α-mode is absent). At rather high rf voltage when a sufficiently large number of high energy electrons appear in the discharge, an intense dissociation of gas molecules via electron impact begins, and the discharge experiences a transition to the dissociative δ-mode. The dissociation products of NF3 and SiH4 molecules possess lower ionization potentials, and they form an easily ionized admixture to the main gas. At higher rf voltages when near-electrode sheaths are broken down, the discharge experiences a transition to the strong-current γ -mode